Abrasive articles and method of making



United States Pa to 2,711,365 ABRASIVE ARTICLES AND METHOD OF MAKING James E. Price, Abington, and Kenneth Deane Groves, Bryn Mawr, Pa., assignors to American Viscose Corporation, Wilmington, Del., a corporation of Delaware No Drawing. Application October 23,1951,

Serial No. 252,792 i 6 Claims. (Cl. 51-298) This invention relates to fibrous structures comprising non-fibrous particulate filling materials andfibers at least 50% by weight of whichare potentially adhesive cotton Wood fibers, cotton, flax,liute, kapok, wool, hair and silk in their natural non-activatablecondition, or it may containartificial or s'yntheticfibers' including cellulosic fibers such as, for example, cellulose hydrate, cellulose esters and mixed cellulose esterswhich are non-thermoplastic and'not rendered tack'yunder the conditions used to bind thefiller particles and ester-coated cotton fibers together, celluloseethers, mixed cellulose ester ethe rs, mixed cellulose ethers, cellulose hydroxy-alkyl ethers, cellulose ,car-;

boxyalkyl ethers, cellulose ether-xanthates, fcellulose Xantho-fatty acids, cell'ulose thiourethanes; natural and synthetic rubberand derivatives thereof; fibers made of alg'inic acid, gelatine, casein; and mineral fibers such as those of spun glass, asbestos, mineral wool, and the like;

and fibers made of naturalfand synthetic resins .which are not rendered tacky under the operating conditions emfibers having a cellulose ester firmly adhered to their surfaces, fibers in the product being bonded together by the cellulose ester. t

In the production offibers or othershaped articles from cellulose acetate and other fiber-forming organic acid esters of cellulose it is the common practice to filter the ester dope through cotton battingbefore it is delivered to the spinnerets or other forming devices. As a result of filtering the ester dope, the cotton fibers of the batting are impregnated by the ester, some of which adheres to the fibers. The cotton batting eventually be-,

comes clogged by the retained ester and has to be discarded. Such discarded ester-impregnated have heretofore been regarded as waste.

We have found that although cotton fibers are not per se potentially adhesive fibers and cannot'be ac'tivated to a tacky or adhesive condition, the non-fibrous cellulose acetate or similar cellulose ester adhering to the surfaces stituted by a compacted, felt-like fibrous structureformed of or comprising the cotton fibers having the cellulose acetate adhered to their surfaces and particles of a nonfibrous filling material which are distributed substantially uniformly through the matrix. 7, I

The products are made by commingling fibers at least by weight of which are the cotton fibers carrying the cellulose ester and particulate non-fibrous fillingmaterials to obtain an intimate mixture of the fibers and lose ester adhering to the surfaces of the cottonr lfibers, activating the ester to softened or tacky conditionfto bind fibers in the product, anddeactivating'the ester to set the fibers firmly in the bonded relation, the filler particles being held securely in the product 'by'.the bonded fibers.

The final product may consist wholly of the cotton fibers carrying the cellulose ester and'the filler particles, or it may also contain a small proportion of fibers which filter media are not themselves activatable to the tacky condition'and which are not coated or impregnated with an activatable material, as well as other types of fibers 'which are activatable to tacky condition, i. .e., fibers which are potentially adhesive but different from the cotton fibers carrying the'ester.

For example, in addition to "the filler particles and the cotton fibers coated or impregnated with cellulose acetate or the like, the products may contain a given proportion, that is, up to 50% based on the total weight of the fibers in the product, of natural fibers, such as, for example,

v as, for example, polymerized ,butadiene,

ployed, as well 'a'sfibers andfilaments obtained by slitph ne- The ting, cutting, or shreddingInon-fibrous films-such as celloup to 50% basedon'the total weight of the fibers inithe product, may be composed of a wide variety of materials and may comprise anytr'naterial-capable of being formed into fibers which, have an inherent tackiness under con ditionssuch that those fibers and-the cellulose ester adhered to the 'surfacesof the 'cot-ton fibers arejrenderedfl tacky without damage'rto'the cotton-fibers or" to any other non-adhesive fibers present, and whieh areno-ttacky at room temperature. Examples of the potentially adhesive fibers which ma be presentiare-thermoplasticfibers such as thoseoftcellulose acetateor, othercellulos'e esters and '7 others, or r'nfixed cellulose esterss'u'ch'as cellulose "acetatepropion'atejor cellulose 'acetate butyrate, t-in plasticized condition; also. resins as, for example, cheap natural resins such as shellac, dammar, copal and the like, and synthetic resins" which are either permanently thermoplastic or 1 thermo'setting butinthe thermoplastic state at theatime they'a16. mixed'with the cellulose-ester coated fibers fwhich arethe,principal'binding fibers in the product, thesyn fbei'ng termed by the polymerization orcon-- Y densation of various organic-compounds such as con: marone, indene or'related hydrocarbons, vinyl compounds,

the'tic resins styrene, sterols, aldehydes,"furfural, ke'tones, urea, thio-1 urea;- phenol-aldehyde resins. either uhmodified or modi-f tied with oils; urea-aldehyde resins;'sulfonamide-aldehyde resins; polyhydric alcohol-polybasic acid resins; drying oil-modified alkyd resins; resins fgn'med by the polymerizar tio'n'of "acrylic acidor itshomologues or derivatives; sul

furolefine'resins; resins-formed from dicarboxylic acids anddiaminesc (nylon type) or fromldicarboxylic acids andpolyethylene glycolst-Dacron type); synthetic rubparticles in which the latter are incontact with the ccllubers and rubber substitutes,1herein called resins, such olefinc polysulfide s, fisobutylene polymers,

polymeric substances obtained by copolymerizing or interpolymerizing two or more copolymerizable monomers,

such ascopolymers of a vinyl halide and a vinyl organic acid ester, e. g'., copolymers of vinylchloride and vinyl acetate, copolymers of a vinyl compound and a 'styrol compound, copolymers oi acrylonitrile with one or more other mono-ethylenically unsaturated monomers "which are copolymerizable with acrylonitrile, and also a mixture of-resins, :such as amixture of poly-olefine resins and the total of such other fibersincluding both non-adhesive Patented June 21, 1955 potentially adhesive fibers which may be present withthe cellulose ester treated cottonfibers'in anamount V v chloroprene polymers; polyethylene; and fibers formedfrom a resin comprising crepe rubber,

-53 and potentially adhesive fibers, is not in excess of 50% by weight, based on the total weight of the fibers in the product.

The fibers and particles may be bonded together solely by activation of the cellulose ester on the surfaces of the cotton fibers and of any fibers present in the product which are per se potentially activatable to the tacky or adhesive condition, or the product may also comprise a nonfibrous thermosetting resin which is applied to the mixed fibers and filler particles in liquid condition, and brought to the hardened, thermoset condition in situ in the product. Any of the thermosetting resins commonly used in the molding art may be used but preferably the thermosetting resin is a melamine-formaldehyde resin or a phenol-formaldehyde resin. setting resin will depend on the type of fibers mixed with the cellulose ester-treated cotton fibers, if such other fibers are used, since some of the thermosetting resins are more satisfactory for use with certain types of potentially adhesive fibers than with others. For example, when fibers of a potentially adhesive vinyl resin, such as fibers of vinyl chloride-vinyl acetate copolymers are present in addition to the cotton fibers carrying the cellulose ester, it is preferred to avoid the use of phenolic resins as extraneous binders, melamine-formaldehyde resins having been found to be more satisfactory. The use of the melamine-formaldehyde or phenol-formaldehyde resin in conjunction with the cotton fibers having the cellulose ester coating or carrying adhered particles of the cellulose ester on their surfaces improves the strength of the product by reinforcing the bonds between the fibers and between the fibers and filler particles.

The choice of non-fibrous filler for admixture with the fibers will be determined entirely by the purpose for which the final product is intended since the filler will, of course, have a definite effect on the physical properties of the final product. Thus, the filler may serve simply to fill the interstitial spaces between fibers in the product, thereby increasing the density of the product and also increasing its mechanical and impact strength; or it may also improve or modify the properties of the product in other respects, for instance the conductivity of the product for heat or electricity; its resistance to shock or chemical reagents; its abrasiveness, etc. The filler may be a pigment, such as chromium oxide, titanium oxide, iron oxide pigments, barium sulfate, carbon black, graphite, zinc oxide, etc. Further the filler may be a special absorbent substance such as activated magnesium silicate, activated carbon, silica gel, activated alumina, fullers earth, activated bleaching clay, activated bauxite, French chalk or r the like. Or the filler may be a substance such as asbestos powder, mica, sand, rotten stone, clay, brick dust, diatomaceous earth, talcum, slate powder, etc.

In the preferred embodiment of the invention, however, the filler is an abrasive material and the final product is adapted to use as an abrading or polishing device. Any of the abrasives in common use may be used, including silicon carbide, boron carbide, fused aluminum oxide, fiint, pumice, Carborundum, emery, rouge, and similar materials. The size of the abrasive particles may vary from the finest polishing or bufiing powder to the coarser grit sizes used in grinding.

The cotton fibers having the cellulose ester adhered to their surfaces may be obtained by drying the cotton batting used in filtering the cellulose ester after it has become clogged and useless as a filter, and then grinding, shredding or cutting the batting to produce a mass of loose cotton fibers the surfaces of which are coated with the ester or which have particles or discrete deposits of the cellulose ester firmly adhered to their surfaces.

The filler particles and fibers may be commingled and formed into shaped articles in any suitable manner. For example, the fibers and filler particles may be commingled by blowing them with air or any other gaseous or vaporous but preferably gaseous medium into a common mixing The choice of the thermo- 5. and depositing chamber, and permitting the thus freely intermixed fibers and particles of filler to settle out on a collecting device.

After association of the fibers and non-fibrous filler particles and collection of the mixture, the product is compacted and the cellulose ester adhering to the surfaces of the cotton fibers, as well as any fibers of the potentially adhesive type present in the mixture, are activated by heat or solvent to effect a firm binding of the fibers and filler particles. After the activation and compaction, which operations may be performed simultaneously, the activated ester film or deposits on the surfaces of the cotton fibers, and any activated fibers present, are deactivated to non-adhesive condition to fix the fibers and filler particles in the new relationship. If activation has been accomplished by heat, deactivation may be effected by heating for a prolonged period or by cooling. If activation is by means of a solvent for the cellulose ester, for instance acetone in the case of cellulose acetate, deactivation may involve extraction of the solvent as by washing, evaporation, or decomposition.

In a preferred embodiment of the invention in which the product comprises the filler particles, the cotton fibers carrying the adhered cellulose ester, and a thermosetting resin of the type of melamine-formaldehyde and phenolformaldehyde resins, the presently preferred procedure is to first thoroughly wet the filler particles with a solution of the thermosetting resin-forming constituents or with the liquid resin precondensate, in a Hobart mixer, and then slowly add the fibers carrying the cellulose ester or a mixture of such fibers with not more than 50% by weight of other fibers to the wet particles, with mixing. The short fibers tend to curl around the resin-treated filler particles and cling to the surfaces of the particles. The fibers, filler particles and thermosetting resin are uniformly distributed through the resulting mass which is then compacted under heat and pressure to the desired shape.

The mass may be shaped to the desired form in any suitable manner. Thus, the mixture of fibers and filler particles may be introduced into a stationary mold of the desired shape and subjected to heat and pressure in the mold, or it may be continuously forced through a heated extrusion device to produce rods and tubes having any desired cross-section, for example, circular or oval.

Under the heat and pressure of the molding conditions,

fibers in the mass are bonded together as a result of the adhesiveness of the cellulose ester. The mass obtained by grinding the cotton batting impregnated or saturated with the cellulose ester may comprise loose discreteparticles of the ester which may be present in the ground material mixed with the filler particles. Any such discrete fragments of the cellulose ester in the mass molded are activated during the molding step. The activated cellulose ester blinds fibers in the product Wherever the ester occurs in it. The products are cooled in or after removal from the mold to deactivate the ester and fix the bonded fibers and filler particles in the bonded relation. Thermosetting resin constituents, if present in the mass molded, are further reacted during the molding step with setting up of the resin which flows to form a film around and between the fibers and filler particles, which film increases the strength of the product. Molded articles comprising the thermosetting resin may be baked at elevated temperatures to fix the resin in the thermoset condition and drive off any water or volatile substances present in the products, the baking being performed at temperatures below the molding temperature.

The present invention may be adapted to the produc-- tion of compacted fibrous structures comprising particles of filling material and discontinuous fibers of any suitable length. However, in the preferred embodiment the fibers are short, of the order of one-half to one millimeter in length. The cotton batting may be ground (shredded, cut or otherwise broken up) to obtain fibers having aj length in the preferred range and having the cellulose ester adhered to their surfaces as a coating or film, or in the form of discrete particles.

In a preferred embodiment, a reinforcing fabric is associated with the molded fibrous article. comprising the discontinuous fibers and filler particles, a fabric, and preferably a woven fabric, comprising a thermoplastic resin or a thermosetting resin in the thermoplastic state being placed over the mass of fibers and filler particles inthe mold and bonded to the. mass during the molding operation. Fabric woven'of nylon yarns maybe molded with the mass and bonded to it. The nylon fabric may be coated with a solution of the constituents of a thermosetting resin, or with a partially condensed thermosetting resin, the constituents of the thermosetting resin being reacted while the fabric is in contact with the, mass of discontinuous fibers and particulate filler. The fabric need not be woven or otherwise fabricated from yarns I of a thermoplastic resin, since fabrics formed from other types of yarns may be coated or impregnated with a thermoplastic resin or with the constituents of the thermosetting resinand molded with the mass of discontinuous fibers and filler particles.

The invention is particularly adapted to the production of various types of abrasive and polishing devices suitable for abrading purposes, including grinding and polishing wheels, abrasive disks, sanding and polishing belts, blocks, pads, and other shapes. prising the cotton fibers having cellulose acetate adhered to their surfaces, and in which fibers'are bonded together, may be cut into squares or sections of any shape to be used in a manner similar to sand-paper or emery cloth, or they may be cut into narrow strips for various purposes. For instance, such matsor bats, orsegments thereof, may be glued or otherwise attached to a hand block or the like. Short lengths or pieces of the abrasive mats may be placed in a tumbling barrel with articles I. a 6 provides abrasiveand other molded, devices which exhibit excellent mechanical and impactst'rength, at compara- V tively little expense.

Thefollowing examples are given to illustrate specific embodiments of the invention.

Example I Q l A molding masscomprising, on the weight of the mass, of cotton :fibers having a'length'of about one-half millimeter and the surfaces of which carrieda film or discrete particles of'cellulose acetate (obtainediby dry'.- ing and grinding acotton batting which had been used r to filter a secondary cellulose acetate dope andwhich was saturated with the dope), 65%1of abrasive grit, and 10% of a phenol-formaldehyde resin precondensa'te was obtainedfas follows: 1 I

The'abrasive particles were placed in a Hobart mi'xer An aqueous solution of the liquid resin precon densate containing 85% solids was added. Afterfthorough mix-" ing to wet' the surfaces; of theabrasive particles withthe resin, the cotton fibers having cellulose acetate adhered Mats or bats cornto their surfaces were added slowly and thoroughly mixed with, the abrasive. The'mass" was thenplaced'in'the V cavity of the female member ofa' mold 'providedwith a centrally disposed projection and of the typefcommonly.

*used in molding abrasive wheels. An annular woven nylon'fabric was slipped 'over the central projection of the mold member. The 'male mold member provided ,with a centrally disposed hollow projectionlwas' placed 1 over the female mold member and pressed upon the nylon 1 fabric'andthe mixture .of fibers and filler particles; Both 1 members ofthe moldwere 'heated'to 350 F. The mass was heated at350I.fF.'for ten, minutes under a pressure approximately 3000 lbs'.-p'er sq. in. cooled to deactivate 1 the cellulose ester, and the molded product, a wheel having adiameter of.9" and; a central bore having a diameter'of A, was removed. It was placed in a hot which are to be finished, in order to cut down the edges or otherwise polish or finish the exterior of the articles. By incorporating other types of fibers, either potentially adhesive fibers or non-adhesive fibers, or by incorporating both types of fibers with the mass comprising the filler Instead of abrasive particles, particulate-filling mate- 0 rials of other kinds may be mixed with the fibers and molded to obtain products' having characteristics which adapt them to special uses. For example, molded devices such as washers, caster wheels, Wheels for vacuum cleaners, carpet sweepers or the like may be obtained. The use of graphite or similar lubricious types of filler particles results in products which are useful as oilless" bearings, washers, packings, etc; For these lastmentioned purposes, the product preferably comprises the thermosetting resin.

The proportion of cotton fibers having the cellulose ester adhered to theirsurfaces in the product may vary but is usually between 5 and preferably about.25% by weight. varied depending upon the type of filler selected and the intended uses of the product, butis usually between 50 and 95% preferably about 65% by weight, when the product consists of the cotton fibers carrying the cellulose ester on their surfaces and the filler. When the product comprises a thermosetting resin, the resin may be present in an amount between 5 and 15% by weight.

By using fibers at least 50% by weight of which are .air 'oven and baked at a temperature of 250,F. for four hours to complete the conversion of the phenoleformaldesolids (available commercially under thejtrade designa- I 'tion-Resamine804"); and thecotton fibers and cohyde resin to the thermoset, insoluble condition.

Example 11 'A molding mass comprising,--on the weight of the i mass, 20% of cottonifibers'about /2 min. long and .hav-

abrasive grit;.and 10% of a precondensate of a melamineformaldehyde resin, was obtained as follows: i y

The abrasive grit was thoroughly mixedwith an aqueous solution of the resin precondensate containing 70% polymer fibers were added. After thorough mixing, the mass was molded to obtain 'a Wheel which was baked in a hot air oven, all as in -Example I.

Example 111' I weight of finely powdered pumice with 50%1by'weight of the cotton fibers obtained by shredding a dried, cellu- The proportion of filler particles may be lose acetate-impregnated cotton batting filter, to'obtain a loosernassof fibers having a length of about 1 mm; The mass was molded as in Example I to obtain a wheel in which the fibers were bonded together Wherever the I cellulose=acetate occurred in it',.and"cooled to deactivate the ester and fix the fibers and-pumice particles in the wheel. r

' Since changes may be made in practicing the invention without departing fromt he spirit and scope thereof, it is to be understood that the foregoing description'and examples areillus'trative only, gan d thatthe invention'is except as defined by .theappended;

claims. v

We claim:

1. A method of making a felt-like, compacted fibrous product which comprises wetting particles of a nonfibrous filler material with a liquid comprising a precondensate of a thermosetting resin, associating the Wet filler particles with discontinuous cotton fibers having a non-fibrous cellulose organic acid ester adhered to their surfaces, heating the mass of fibers and filler particles to a temperature at which the cellulose ester is rendered adhesive, subjecting the mass to pressure while the ester is in the adhesive condition to obtain a product in which fibers are bonded together by the ester and in which the filler particles are fixed in a condition of substantially uniform distribution by the bonded fibers and by the resin, cooling the product, and heating the product at a temperature below the temperature at which the ester is rendered adhesive to convert the resin to insoluble, thermoset condition.

2. The method of making a felt-like, compacted fibrous product as defined in claim 1 wherein the thermosetting =1 resin is a phenol-formaldehyde resin.

3. The method of making a felt-like, compacted fibrous product as defined in claim 1 wherein the thermosetting resin is a melamine-formaldehyde resin.

4. A felt-like, compacted fibrous abrasive wheel comprising 50% to 95% by weight of abrasive particles,

5% to 50% by weight of discontinuous cotton fibers having a non-fibrous cellulose organic acid ester adhered to their surfaces, and 5% to 15% by weight of a thermosetting resin in the thermoset condition in contact with the abrasive particles, the fibers being bonded together, at least some of the fibers being bonded together by the cellulose ester adhering to their surfaces, and the abrasive particles being fixed in a condition of substantially uniform distribution throughout the wheel by the bonded fibers and by the thermoset resin.

5 A felt-like, compacted fibrous abrasive wheel as defined in claim 2 wherein the thermosetting resin is a phenol-formaldehyde resin.

6. A felt-like, compacted fibrous abrasive wheel as defined in claim 2 wherein the thermosetting resin is a melamine-formaldehyde resin.

References Cited in the file of this patent UNITED STATES PATENTS 2,398,408 Buell Apr. 16, 1946 2,404,207 Ball July 16, 1946 2,432,091 England Dec. 9, 1947 2,483,406 Francis Oct. 4, 1949 2,527,628 Francis, Jr. Oct. 31, 1950 2,543,101 Francis Feb. 27, 1951 

1. A METHOD OF MAKING A FELT-LIKE COMPACTED FIBROUS PRODUCT WHICH COMPRISES WETTING PARTICLES OF A NONFIBROUS FILLER MATERIAL WITH A LIQUID COMPRISING A PRECONDENSATED OF A THERMOSETTING RESIN, ASSOCIATING THE WET FILLER PARTICLES WITH DISCONTINUOUS COTTON FIBERS HAVING A NON-FIBROUS CELLULOSE ORGANIC ACID ESTER ADHERED TO THEIR SURFACES, HEATING THE MASS OF FIBERS AND FILLER PARTICLES TO A TEMPERATURE AT WHICH THE CELLULOSE ESTER IS RENDERED ADHESIVE, SUBJECTING THE MASS TO PRESSURE WHILE THE ESTER IS IN THE ADHESIVE CONDITION TO OBTAIN A PRODUCT IN WHICH FIBERS ARE BONDED TOGETHER BY THE ESTER AND IN WHICH THE FILLER PARTICLES ARE FIXED IN A CONDITION OF SUBSTANTIALLY UNIFORM DISTRIBUTION BY THE BONDED FIBERS AND BY THE RESIN, COOLING THE PRODUCT, AND HEATING THE PRODUCT AT A TEMPERATURE BELOW THE TEMPERATURE AT WHICH THE ESTER IS RENDERED ADHESIVE TO CONVERT THE RESIN TO INSOLUBLE, THERMOSET CONDITION. 